488 ON THE PHYSICAL STRUCTURE 



its southeastern border,-in the Bhic ridge and great valley ad- 

 joining, there exists a general ' tendency to an oblique folding or 

 inversion of the strata, though this condition is less predominant 

 than in the two before-mentioned straight portions of the chain, 

 namely, the Susquehanna and Hudson divisions. In other words, 

 the rocks are less completely folded, many perpendicular and 

 some northwestern dips occurring, to form the northwest side of 

 the arches, and, as we advance beyond the valley, the normal 

 curvatures become the prevailing ones. In accordance with this 

 general condition of things, the great valley contains a long cen- 

 tral belt of the middle Appalachian formations, included in a deep 

 trough, a feature that could not exist, if the synclinal foldings 

 were as compressed as in the other more inverted distiicts. This 

 less closely folded state of the rocks appears to extend entirely 

 across the whole undulated belt, the breadth of which, from the 

 Blue ridge to the valley of the Monongahela, is about one hun- 

 dred and ten miles. Such a feature seems to imply a less ener- 

 getic disturbing force in this belt than in the district of curving 

 axes adjoining it on the north, where the rocks in the valley are 

 mu^ch inverted ; and this inference is supported by the fact of the 

 very rare appearance, at the surface, of those lower rocks, the older 

 Appalachian limestone, for example, which occupy anticlinal 

 tracts in the curving belt, and form a conspicuous feature of it. 



6. James River Division. This district, sharing with the rest 

 all their essential structural features, and displaying, as formerly 

 mentioned, especially in its valley portion, much irregularity in 

 the strike of its strata, and the direction of its generally short axes, 

 is remarkable for a confused blending of the various kinds of 

 flexure, even within a narrow breadth, and for the passage, more 

 frequently than in the previous division, of the folded and inverted 

 flexures into faults. The great valley is here occupied, in part, 

 by the extensive synclinal range of the Short Hill, and the wide, 

 irregular trough, including the Catawba and Fort Lewis moun- 

 tains, as well as by other minor ridges of the superior rocks, and 

 is marked by the occurrence of a long line of fault, accompanied 

 by inversion, along the southeast side of the Fort Lewis moun- 

 tain, and by the prolongation, in a variety of curious phases, of 



